Work out your upfront, monthly and first-year costs →
The core kit
| Item | What it’s for | What to check when buying | Cost note |
|---|---|---|---|
| Salt mix | The supply you’ll buy most often | Compare how many litres it makes, not just the bucket weight | £69.99–£89.99 for common 22–25 kg packs |
| RODI storage container | Holds RODI water until you mix it | Food-safe, with a lid, and big enough for a normal water change | One-off cost; varies by size and shop |
| Mixing container and pump | Keeps the saltwater moving while it mixes | Used only for this, clean, and powerful enough for the container | Bought once; keep it away from dirty tank water |
| Heater | Brings the new water close to tank temperature | Choose one with a guard, and check it with a separate thermometer | The heater plus the electricity to run it |
| Refractometer or salinity meter | Checks the salinity before the water goes in | Calibrate with the right fluid, and recheck stored water | Calibration fluid runs out, and it’s easy to forget |
| Tubing, siphon and spare seals | Moves water without leaks or spills | Keep spares so a split hose doesn’t stop a water change | Small, regular cost; fittings for specific models can cost more |
What’s worth keeping spare?
Keep spare tubing, a basic transfer pump or siphon, replacement seals and calibration fluid. If your mixing pump is the only way to make water, a broken impeller can turn a routine change into an overnight wait. The right backup is the smallest one that stops you improvising with dirty or untested kit.
Label what’s clean
Mark every container, hose and pump as either clean (RODI and new saltwater) or dirty (water from the tank). It’s a cheap way to avoid contamination. Keep your dry salt with its batch details, and note the date you open each new bucket, so you can trace an odd result back to a product or batch.
Budget for the year, not the basket
Start with how many litres you change in a year and multiply by your salt cost per litre. Then add calibration fluid, replacement tubing, electricity and a little extra for worn-out pumps or containers. That keeps the ongoing cost in view when you’re comparing a cheap salt with a pricier one that might change your dosing or mixing routine.
Sources and limits
We checked salt yields and mixing guidance against Aquaforest’s official instructions and Red Sea’s mixing guide. Prices in our related guides are current UK examples, not a full market survey. We haven’t tested any of the equipment ourselves.
THE SHORT ANSWER
A smooth water change depends on the small stuff
A water change needs more than salt. You’ll want RODI filtration, a suitable mixing container, a pump to circulate it, perhaps a heater, a way to measure salinity plus calibration fluid, a hose or pump to move water, towels, cleaning tools and any tests the change calls for. The things you’ll keep buying include salt, filters, resin, test reagents and replacement tubing or pump parts.
A dedicated, labelled kit cuts the risk of contamination and makes the routine easy to repeat. Keep enough supplies for your next planned change plus an emergency one, but don’t stockpile so much opened salt or reagent that damp and expiry dates turn it into waste.
STEP BY STEP
How to do it
- 01
Keep clean and dirty tools apart
Use separate equipment for mixing and for moving tank water. Don’t put algae scrapers, siphons or used towels back with your clean-water kit.
- 02
Check your supplies first
Make sure you have salt, enough RODI water, calibration fluid and working pumps before you take any water out of the tank.
- 03
Make and check the new water
Match the salinity and temperature, and test other readings if the change is large or you’re using a new salt.
- 04
Clean, dry and restock
Rinse the kit, let it dry, note what supplies are left, and replace anything that won’t last until next time.
YOUR SITUATION
What to do in your situation
Familiar routine and a steady batch of salt
Use your usual kit and note anything out of the ordinary.
The new water’s chemistry could differ noticeably
Test the new batch more thoroughly, and split it into several smaller changes if needed.
Rushing makes mistakes more likely
Follow a checklist you wrote in advance and use supplies you’ve stored safely, rather than improvising.
COMMON MISTAKES
Mistakes to avoid
Taking tank water out first
If the mixing pump fails, you’re out of salt or the batch is wrong, you suddenly have an emergency.
Using household containers
Traces of detergent, cleaning products or food can contaminate reef water.
Letting calibration fluid go out of date
A refractometer can look precise while a bad reference fluid throws off every batch.
WORKED EXAMPLE
Setting up a compact water change station
A nano reefer keeps one 30-litre lidded container, a small mixing pump, a short transfer hose, a refractometer, calibration fluid, scales and towels together. Salt and RODI spare parts are stored dry nearby, and the gravel siphon and dirty-water bucket are clearly kept apart.
Before every change, they make and check the new water before taking any out of the tank. Afterwards, they note how much salt is left and when they last calibrated the refractometer. Nothing gets forgotten, and they don’t need a fish room to do it.
BEFORE YOU CHANGE ANYTHING
Write down where you’re starting from
Note the date, the equipment or product you’re using, how you measured and the conditions behind every important number. Say whether a volume is the tank’s label figure or your real net water; whether a flow is the box rating or what actually comes out; and, for test results, the salinity, test kit and time of day. A precise-looking number is useless once you’ve forgotten where it came from.
Change one thing at a time, and decide in advance what improvement will look like: a steady test trend, less detritus, a more stable temperature, a quieter tank or a lower running cost. One reading, or one good day, isn’t a trend, and a setting copied from someone else’s tank isn’t proof it suits yours. The free Reef Companion keeps your tests, maintenance and changes in one dated log, so you can see cause and effect.
MAKING CHANGES SAFELY
Protect your tank while you make the change
Take a baseline
Measure before you install equipment, change your chemistry or alter your routine. Take photos if placement matters, and note how your livestock behaves. Without a starting point, you can’t be sure what caused any difference later.
Start small
Begin with a cautious setting or dose, and keep a way back. Hang on to the old equipment until the new one has proved itself, keep your previous schedule, and don’t add livestock at the same time as a big lighting, flow or chemistry change.
Give it the right amount of time
Mechanical problems show up straight away; nutrient and coral responses can take days or weeks. Judge the change over a sensible period, but stop immediately if you see animals in distress, a leak, overheating or an electrical risk.
Afterwards, note the result and decide whether to keep, adjust or undo the change. If the result is unclear, go back to your last stable setup and measure better, rather than piling on another change.
SIX MONTHS ON
Check it’s still the right decision
What made sense on day one can stop working as livestock grows, the room warms up, equipment gets dirty or a routine turns out to be unrealistic. Set a reminder to review it in six months, comparing what you assumed with the reality: water volume, electricity, consumables, noise, cleaning time and test trends.
Test trends, real flow, temperature, light coverage or whatever the change was for
Is it still doing its job, with room to spare?
How often you clean it, how hard it is to reach, calibration drift and missed tasks
Can you keep this up without cutting corners?
Electricity, reagents, filters, spare parts, warranty and downtime
Would you make the same choice knowing the real cost?
If it’s working, you don’t need to replace it; the review simply gives you a reason to keep it, tune it or plan an upgrade before something fails.
KNOW THE LIMITS
When to get expert help
Get product-specific or professional help for anything involving floor loading, household electrics, unsafe plumbing, damaged glass, unexplained livestock deaths, or chemistry you can’t measure reliably. Use a qualified electrician for fixed wiring, and always follow the current safety instructions for your tank, equipment and additives. Never work around damaged cables, swollen batteries, leaking seals or equipment that keeps tripping the electrics.
Your livestock’s needs can also outweigh general equipment advice. Check adult size, behaviour, disease risk and each species’ light, flow and feeding needs with reputable care guides before you buy. This guide explains the equipment decision; it can’t guarantee the result for every animal or tank.
COMMON QUESTIONS
Frequently asked questions
How much spare salt should I keep?
Enough for your normal changes plus an emergency one, balanced against keeping it dry and your budget.
Do I need a heater for mixing water?
It depends on your salt’s instructions and how different the temperature is from your tank. Don’t heat it for longer than you need to.
Can one pump mix and move water?
Yes, if it’s suitable, clean and set up safely. A spare, or a separate way to move water, means one failure won’t stop you.